This work plan management system is provided with a component replenishment management unit for managing a plan for component replenishment work to be performed on component supply devices; and an ancillary work management unit for managing a plan for ancillary work. The component replenishment management unit includes a component supply monitoring unit and a replenishment target specifying unit. The component supply monitoring unit specifies, for each of the component supply devices, replenishment possibility time windows during which component replenishment work is possible. The replenishment target specifying unit recognizes overlapping replenishment time windows in which the individual replenishment possibility time windows overlap, and specifies component supply devices on which it is possible to perform component replenishment work during the overlapping replenishment time windows. The ancillary work management unit specifies ancillary work that is to be started during the overlapping replenishment time windows.